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| Home > Publications database > Light scattering and microwave absorption on spinwaves in thin ferromagnetic films |
| Home > Publications database > Light scattering and microwave absorption on spinwaves in thin ferromagnetic films |
| Book/Report | FZJ-2018-02857 |
1988
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18474
Report No.: Juel-2193
Abstract: For the first time ferromagnetic multilayer structures attracted attention in the late sixties. The mass information storage devices, based an magnetic hysteresis effects in the thin films were very promising, but there were difficulties like lack of stability. Multilayer structures offered one way to modify materials properties$^{(1)}$. Results were not satisfactory as at that time the thin metal films suffered from their bad quality, allowing silicon technology to Lake the lead.Therefore it seems not to be very surprising that a new wave of interest in multilayers of ferromagnetic materials has followed tremendous progress in their technology. Procedures like molecular beam epitaxy (MBE), or various sputtering techniques count for it. They allow for growing of very good quality polycrystalline or single crystal thin films and so called artificial structures$^{(2)}$. In the case of ferromagnets they can consist of layers of different ferromagnets deposited one over the other or layers of ferromagnetic materials separated by nonmagnetic spacers. Thicknesses of such layers may vary now from tenths to hundreths of nanometers.Multilayer structures can have various advantages over single layers. For instance, layers of Co-Cr with uniaxial perpendicular anisotropy, used for perpendicular magnetic recording, improve their properties when built in the structure $N_{80}Fe_{20} \vert$ Co-Cr. Here the Co-Cr film serves as recording medium and the $N_{80}Fe_{20}$ underlayer provides stabilization because of flux closure. Such a double layer allows bit density and stability superior over the single Co-Cr layer$^{(3)}$. The structures investigated in this work are based on Permalloy double layers (nickel-iron alloy in 80% Ni to 20% Fe weight ratio) and different spacer materials. Similar structures have already been investigated before, but new measuring methods suggested to look again into some old, but unsolved problems. Earlier experiments confined themselves mainly to hysteresis and ferromagnetic resonance measurements. One can refer here to Works of Hoffmann et al.$^{(4.5)}$ or Waksmann et al.$^{(6)}$. In this laboratory experiments an multilayers of iron and Permalloy have been carried out by Grünberg and co-workers$^{(7,8,9)}$ by means of Brillouin scattering (BS). Simultaneously, the problem of interlayer magnetic coupling was studied theoretically in the dipolar approximation by Grünberg et al$^{(10)}$. High quality ferromagnetic films have also been grown in this laboratory$^{(8)}$. This provided the perfect background and motivation to continue the first systematic studies of interlayer exchange coupling which Grünberg began an iron double-layers by means of Brillouin scattering. The idea was to start with the very well-known material, Permalloy (Py), taking advantage of its extremely weak magnetostriction and magnetic anisotropy. As a measuring method there was Brillouin scattering already available in this lab, the microwave spectrometer had to be built up. This thesis reports on experimental investigations of Permalloy double layers of Py l A I Py structure, where A is Cr, Cu, V, Pd, Ag, Au and Gd. lt is divided into five main parts dealing with the theory of magnetic excitations in multilayers, experimental apparatus and sample preparation, experimental results and their discussion. A summary and appendix giving explanations for some technical Problems of the microwave measurements close this work.
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